Can anyone explain to me why is Engine and Wing Anti-ice used in aircrafts and on what circumstances are they turned ON? Also what is the principle behind its working? I have often heard pilots mentioning the term Anti-ice using the checklist before take off and approach. Thanks for the explanation.

On the 744 there is an ice detector that will give you an EICAS message of "icing". However, most pilots will turn on the engine heat prior to that. Things like visible moisture, temp below +10C, in flight, visible moisture on the ground with a temb +10C or lower.

On the 744 wing heat is rarely used. One thing to keep in mind is when the flaps are out of the up position, there is no wing heat. The design of the LE is such you don't really have to worry about ice build up. Trying to clear the cobwebs, I think that's true on just about all Boeings I've flown (727/757/747/744).

Some smaller a/c such as turboprops use boots for de-icing. It's an inflatable rubber device that covers the leading edges of wings and stab. When Ice has built up on the leading edge it will inflate, slightly changing its shape and size causing the ice to break up and fall off.

If you look at the center frame of an A320's cockpit windscreen you'll see a small metal rod sticking straight out of it. It looks like a 3 inch long nail.

I asked about this object in this forum a few years ago and was told it's a probe for ice detection.

I can't remember if the pilots simply look at this probe to visually determine if airframe ice is forming or if it's an electronic type of sensor for the EICAS like Philsquares mentioned. Maybe it's electronic and causes only the windscreen heat to automatically turn on if it detects ice.

You can see the A320's ice detector on the windscreen in these 2 photos.

An ice detector works through oscillations. A voltage is applied to the element. This voltage causes the probe to oscillate (no you can't see it). As ice begins to form on the probe, the pitch changes, at a pre-determined threshold, the electronics send a signal to the computers to display "Icing".

Enigine and wing anti-ice use bleed air from the engines to heat the leading edges and the nose cowl to PREVENT icing. They should be turned on prior to any icing indication in the cockpit.

An ice detector works through oscillations
These are way cool as to how they work..!! PFM as we call it.

Most all leading edge and engine inlet de-icing systems are on all the times as long as the engines are running. Some times there will be a switch that opens the valve once the aircraft becomes airborne. As many pilots will tell you, you can icing 12 months of the year under the right conditions. Just a few weeks ago I was flying into Nashville and was in snow and ice all the way down to about 5000ft... once on the ground the temperature 65 and rain.

Engine de-icing is a little different then inlet de-icing where hot bleed air passes through the inner engine guide vanes. This is controlled by a switch in the cockpit when icing conditions are present. This prevents ice from forming or being ingested into the core engine.

"It's not the size of the dog in the fight, but the size of the fight in the dog"

Engine bleed air is taken from the engine and ducted to the leading edge via ducts. At intervals along the leading edge there are tap off that lead to "picolo tubes" (tubes which are perforated), these tubes distribute the hot air along the leading edge. The system is monitored by overtemp switches. If the leading edge gets too hot, the switches will shut down the system.

The wing anti-ice and engine anti-ice are most certainly not left on at all times. They are controlled exclusively from the flight deck with air/ground interrupt on the wing system. You don't want that operating on the ground.

The system pulls alot of air off the engines and would decrease engine performance and increase fuel consumption.

True, icing conditions can occur any time of the year, but operating the system when not required is a waste.

General disclaimer: This is true on the aircraft I'm familiar with (B727, B757/B767, B747, DC-8)

The wing heat is rarely used on aircraft such as the 747-400. One of the system designs is that with extension of the leading edges, the hot bleed air is then prevented from flowing into the leading edge, so no anti-ice. The design of the wing is such that any ice will break off relatively quickly.

The wings are not heated at all times as a prior poster wrote. In fact, the engine heat is not on at all times either.

Since most of the jet's cruise above FL300 the temperatures in those areas are in the -40 to -70 ranges. So is it not necessary to switch on Engine and Wing Anti ice during these conditions? Also as the aircraft levels above FL300 does the low temperatures causes any change in properties of the fuel or the oil system used? What sorts of oils are used in Airbus and Boeings for hydraulics and Engine?

The air is pretty dry att cruising altitudes so icing there isn't a problem. However, the low temps at cruise cools the fuel in the wings to very low temperatures and when descending through humid air the cold wing will cause ice to build up quickly.

Does this cold fuel in cruise conditions make some difference in engine output? Also what is the freezing point of these Jet A1 and other kinds of fuel used for aviation purposes? Is there any specific additives added to fuels of aircrafts which fly over the North Pole?

Don't know the exact figures, but the fuel increases its temp when it goes through the fuel pumps and enters the engine so I can't imaginge it makes a difference. For polar routes I don't know, but I recall seing a thread here not so long ago..

Some aircraft also have a fuel heat system installed in conjunction with an fuel icing detection system. The detection system is basically a differential pressure switch across the filter. If ice particles start to clog the filter the switch will close and the light on the flight deck will illuminate. the flight crew will turn on fuel heat. This will typically open a bleed valve which will allow hot air rto pass through a heat exchanger installed on the engine. The system is seldom used because very hot fuel can present a whole set of problems in an engine.

Another note about fuel. Most engines I'm familiar with have a fuel/oil heat exchanger. The primary function of this heat exchanger is to cool the oil, but an added effect is that the fuel is warmed on its way to the main engine fuel pump.

As to hydraulic fluid, it is typically cooled in flight using surface heat exchangers in the fuel tanks.

Air2gxs & Staffan. Thanks for the explanation. Well I was thinking of asking about that heat exchanger but you guys have mentioned it even before I asked. Well the heat exchanging- Is it done by passing two lines near by each other so that one carries hot gases and the other carries the cold oil and conduction of heat from the hot line to the cold line takes place.

Ok Sir you must be right with the above one. Thanx. Sir lubrication for the engine is a must right? So how is the lubrication done? Is it forced lubrication used to lubricate the engine. Also could you please tell me where the oil storage tank is situated normally in Airbus and Boeing how much quantity of oil will be there in the tank and what is its rate of its consumption? Now we see aircrafts being refueled but never seen one oiled. Well if you know what sort of oil is used then it would be great.

On the B737s Anti Ice consists of WTAI ie Wing Thermal Antiincing,Engine Antiicing,Heating elements in Pitot-static probes,Windshields & heated drain probes.
Remember Antiice is different from De-Icing.Antiicing prevents the formation of Ice,De-Icing removes formed Ice.Expander boots on LE of some Turboprobs are Deicers.
Wing thermal A/I uses hot bleed air from the Engines & ducted along the LE of the Wings to melt out any Ice formation giving a smooth LE surface.
The Engine A/I uses same bleed air to warm certain areas of the Engine to prevent Icing.
The probes,windshield & drains have heater elements built in to prevent Icing.

About Lubrication,Yes the consumption is around 1 qt/hr depending on the Type of Engine.Oil checking is carried out too during refuelling if required,but its a quick job hence you may have not noticed it.The modern Engines have a Dry sump lubrication system where the Oil is located at a different location on the Engine.There are three sub systems Pressure,Scavenge & Breather.Pressure system delivers oil to the bearings,Scavenge returns the oil to the Tank,The breather system maintains the same pressure at both places.

MEL Thanx very much for the explanation. The lubrication brings back a little bit of the worn out portions of the engine back to the sump. Right? .Is it ‘gravity separation’ that prevents these particles from being recalculated during lubrication? Also how is the oil level checked? Is there an oil level indicator and where is it located in 737’s.And what sort of the oil is used for lubrication?

George.
If I understood your question right.We use Mobil jet II.
Yes Oil does bring back worn parts if they occur to the tank,hence there are Magnetic Chip Detectors located in the Oil return/Pressure path.Which pick up metal shavings & help in troubleshooting & Condition monitoring of the Engine.
Oil can be checked thru the gages in the cockpit,signal sent via Capacitance probe fitted to the tank,or Physically by a Dipstick attached to the tank cap or a Sight gage ie a Transparent port on the Tank.
The Oil flow is regulated by Pr & Scavenge pumps.
regds
MEL

Oil consumption varies by engine type. Apparently Hawk works on some older engine types, 1qt/hr is very high for modern, ETOPS approved engines. We are rarely oiling them.

The B767 (CF6) AMM states that the normal consumption is under .25 qts/hr and that any consumption above .55 qts/hr requires correction.

The actual particle seperation is performed by a filter. The magnetic chip detectors just collect magnetic fragments which can be analyzed to determine if the bearings are failing. There are non-magnetic and non-metallic components in the engine that can only be be captured by a filter element.

25 Santhosh
: Yep Sir I have heard from pilots flying A330 that oil level is not much of a concern as its consumption is generally very little. Well George as you s

26 Air2gxs
: Well the first thing done is an inspection for external oil leaks. If no leaks are found, then it is a true consumption problem; the oil is being cons

27 Santhosh
: Ok Sir thanx very much for the information. Sincerely, George